Servers at television networks and banks in South Korea were hacked. / Ahn Young-joon, AP

by Calum MacLeod, USA TODAY

by Calum MacLeod, USA TODAY

BEIJING - A cyberattack that caused computer networks at South Korean banks and television networks to crash Wednesday afternoon originated with a Chinese Internet address, South Korea's telecom regulator said Thursday.

The state-run Korea Communications Commission said its initial analysis found that a Chinese address created the malicious code in the server of one of the banks, Nonghyup, where computers crashed.

After the shutdown, suspicion for the source of the hacking campaign fell quickly on North Korea, which has hit South Korean targets with cyberattacks in recent years and which has threatened Seoul with attack in recent days because of anger over U.N. sanctions imposed for its Feb. 12 nuclear test. South Korea police and government officials declined to blame the North as they launched an investigation into the attack.

It's too early to assign blame to China or North Korea, since Internet addresses can easily be manipulated.

Screens went blank with skulls popping up on the screens of some computers - a strong indication that hackers planted a malicious code in South Korean systems, the state-run Korea Information Security Agency said. Some computers started to get back online more than 2½ hours later.

South Korea's army upgraded its cyberattack readiness by one level, reported the Yonhap news agency.

The computer networks of national broadcasters YTN, MBC and KBS were paralyzed just after 2 p.m. although their TV broadcasts continued. Servers at Shinhan Bank and NongHyup Bank were also affected, shutting some services such as ATMs for a few hours.

Earlier, Seoul's intelligence agency said the North has been engaged in "intensive cyber propaganda activities against South Korea aimed at attacking government policies and fueling social discord," Yonhap reported.

Last week, North Korea accused the USA and South Korea of "intensive and persistent" attacks on its Internet servers, coinciding with U.S.-South Korea military drills, according to the North's official KCNA news agency.

Those drills are underway amid deepening tensions on the often-tense Korean peninsula, still split in two by the Cold War division of the Korean War. After the United Nations imposed sanctions on the North for conducting a nuclear test last month, Pyongyang has threatened attacks on both the U.S. and South Korea.

The U.S. military has recently flown nuclear-capable B-52s in bombing raid practices that the Pentagon said were in response to North Korean "rhetoric." In the North, already a highly militarized society, state media report widespread drills among the civilian population.

Students at the Pyongyang Kaeson Secondary School were pictured in military fatigues on the Rodong Simnun website Wednesday, with the caption "Young students are replete with a firm determination to annihilate the invaders without mercy."

The U.N. sanctions will only succeed in hurting the regime in Pyongyang if China, the North's only significant ally and major supplier of fuel and food, enforces them more strictly than similar sanctions in the past.

China's new President Xi Jinping told his South Korean counterpart Park Geun-hye in a phone call Wednesday that it serves Chinese interests to promote dialogue between North and South Korea, according to China's Foreign Ministry.

The attack comes as U.S. Treasury Secretary Jack Lew completed a two-day visit to Beijing on Wednesday during which he raised the issue of Chinese cyberattacks against the USA with Xi and other Chinese leaders.